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Q: What kind of magnitude is listed in the Basic Data?A: These are usually optical magnitudes taken from
the astronomical literature, and should be understood as being indicative
only. We are adding letters after the magnitudes indicating the band pass
to which the magnitude applies. For example, we use "U", "B", "V", "R", and
"I" for the standard Johnson and/or Cousins magnitudes in the optical; "p" for
photographic magnitudes from e.g. IIa-O or 103a-O plates, "g" for Gunn g-band
magnitudes, "j" for magnitudes from III-aJ plates, "J" for 2MASS near-IR
magnitudes, and so on.
We will eventually have all of NED's Basic Data magnitudes flagged with
the band passes. In the meantime, the magnitude may have already been
included in NED's table of of referenced
Photometric Data.

Q: How do I read a 19-digit REFCODE?A: NED reference codes are 19-character strings of the form:
YYYYPUBLNVVVVMPPPPA

Unused characters are padded with dots ".".
The fields within the string are as follows:

YYYY

The four digits of the year of
publication

PUBLN

The journal code, left-justified
within the five-digit field

The codes for those journals regularly entered into
NED are:

A&A..

Astronomy and Astrophysics

A&AS.

Astronomy and Astrophysics Supplement Series

AJ...

Astronomical Journal

ApJ..

Astrophysical Journal

ApJS.

Astrophysical Journal Supplement Series

ARep.

Astronomy Reports (formerly Soviet Astronomy)

AstL.

Astronomy Letters (formerly Soviet Astronomy
Letters)

Ast..

Astronomy

IAUC.

IAU Circulars

MNRAS

Monthly Notices of the Royal Astronomical Society

Natur

Nature

PASP.

Publications of the Astronomical Society of the
Pacific

PASJ.

Publications of the Astronomical Society of Japan

VVVV

Volume number of the journal,
right-justified within the four-digit field

M

Tie-breaker code. Where ambiguity is
possible (e.g. between the main journal section,

and the "letters" section of a journal), the following
characters or digits in this field break the ambiguity:

L

Letters sections in various journals

p

Pink pages in MNRAS. (changed to "L" in 1993)

1, 2, ..., 9,

Issue numbers 1 through 9, then "a"
through "o", within the same volume of a journal

0, a, b, c,

(e.g. Sky and Telescope, Physics
Today).

..., o

A, B, ...

Issue designations used by the
publisher within the same volume, where each issue starts with page
one.

OR

Two or more articles appearing on the same
page within a single issue of a journal

Q: What do notations such as "NED01", ID", and "NOTES02" mean?A: These are suffixes which we add to a root name to distinguish physically separate objects which do not otherwise carry separate names. For example, UGC 01562 is a double galaxy, but has only one entry in UGC. In order to include both galaxies in NED with unique names, we add the notation "NED01" and "NED02" to "UGC 01562". Similarly, we add "NOTES01" to UGC 01562 to refer to a galaxy included only in the UGC Notes for UGC 01562.

We typically use the "ID" suffix to indicate that a non-optical source (e.g. an infrared source) has been associated with an otherwise unnamed physical object, usually a galaxy. An example is "IRAS 00182+1130". This has been identified as a galaxy, but not given a separate name. The "ID" notation makes it clear that the object has been reclassified from its original type.

Other suffixes that we use include "COM" for a nearby companion, not necessarily physically connected to the main object (e.g. "3C 227 COM01"), "ABS" for an absorption line system seen along the line of sight to a background object (e.g. "[HB89] 1727+502 ABS01"), and "ARC" for gravitationally-lensed arcs usually found in rich clusters (e.g. "ABELL 0164 ARC01").

Q: How often is NED updated?A: Usually three or four times a year. A backup working copy of the database is continually updated and checked for problems and errors before being released.

Q: How complete is NED?A: We have tried to get all data published since 1988 into the database, but we invariably miss some and probably have errors as well. We are also constantly changing and refining the Basic Data so you may not always see the same data from month to month (although if the change is large we will generally include a note to that effect). Also, we scan the refereed literature only in the larger professional journals. Thus, if data are published only in an observatory monograph, only in preprint, only in a conference proceeding, or only in a thesis, we may well not see it. In these cases, we are happy to add the data to NED when you bring it to our attention.

Q: Are the redshifts reported in NED spectroscopic or photometric? And what do the codes following the redshift mean?A: We adopt spectroscopic redshifts whenever they are available. Sometimes, however, only a photometric redshift is available for an object, or the source of a redshift is not clearly stated in the published paper. In those cases, we flag the redshifts if we know that they are not from spectroscopy. It is still possible, however, for photometric
redshifts to slip in unflagged. In cases of doubt, we urge you to go back to the published paper to check the source of the redshifts.

When we can determine from the reference the Quality of a Basic Data redshift, we attach a code to it. Here is a list of the codes:

the redshift of a host galaxy determined from the expansion velocity of a supernova

Q: What is the source of the morphological types in the NED database? Is there a way to find out where the classifications for each galaxy came from?A: Many of the morphological types in NED come from the Third Reference Catalog of Bright Galaxies (RC3). This is essentially the same system as described in the RC2. Both of these texts should be available from your library. We have also added physical classifications from spectroscopy when available (e.g. "Sy1", "BLLAC", "HII", and so forth). These and other classifications come from the literature, but are not yet specifically referenced.

Q: The "Morphology" line of NED's Basic Data sometimes contains abbreviations such as "BCD" and "Sbrst". What exactly do these mean?A: These are usually "standard" abbreviations, taken from the literature, for various sorts of nuclear activity in galaxies. Occasionally, they are simply descriptive abbreviations relating to the morphology of the galaxy. Here is a list:

AGN

active galactic nucleus

BAL

broad absorption line

BEL

broad emission line

BBG

Balmer-break galaxy

BCDG

blue compact dwarf galaxy

BH

black hole

BLAGN

broad-line active galactic nucleus

BLLAC

BL Lacertae-type object

BLAZAR

Strongly variable and optically-polarized QSO or
BL Lac object, often with strong gamma- and X-ray
emission

BlueCG

blue compact galaxy (may be called BCG in
the literature)

BLR

broad line region

BLRG

broad line radio galaxy

BrClG

brightest cluster galaxy (may be called BCG in
the literature)

cD

supergiant galaxy with an extensive envelope in a
cluster

CNELG

compact narrow emission line galaxy

DANS

dwarf amorphous nuclear starburst

DLA

damped Lyman-alpha

DLyA

damped Lyman-alpha

DOG

dust-obscured galaxy

ELG

emission line galaxy

ERO

extremely red object

FSRQ

flat spectrum radio QSO

HEG

high-excitation narrow-line radio galaxy

HEX

high excitation line galaxy

HII

HII-type object

HPQ

high polarization QSO

IFRS

infrared faint radio source

LAE

Lyman-alpha emitter

LBG

Lyman-break galaxy

LCBG

luminous compact blue galaxy

LCG

luminous compact galaxy

LEG

low-excitation narrow-line radio galaxy

LERG

low-excitation radio galaxy (not to be confused
with LIRG)

LEX

low excitation line galaxy

LINER

low-ionization nuclear emission-line region

LIRG

luminous infrared galaxy (not to be confused with
LERG)

LPQ

low-polarization QSO

LSB

low surface brightness

NELG

narrow-emission-line galaxy

NLAGN

narrow-line active galactic nucleus

NLRG

narrow-line radio galaxy

NLSy1

narrow-line Seyfert 1

OFRG

Optically-faint radio galaxy

PAS

passive nucleus

PEG

passive elliptical galaxy

QSO

Quasi-stellar object

RET

retired nucleus

RLG

radio-loud galaxy

RLQ

radio-loud quasar

RQQ

radio-quiet quasar

Sbrst

starburst object

SFRG

Submillimeter-faint, star-forming radio galaxy

Sy1

Seyfert 1

Sy1.2

Seyfert 1.2

Sy1.5

Seyfert 1.5

Sy1.8

Seyfert 1.8

Sy1.9

Seyfert 1.9

Sy2

Seyfert 2

Sy3

Seyfert 3

ULIRG

ultra-luminous infrared galaxy

XBONG

X-ray bright/optically normal galaxy

XMPG

eXtremely Metal-Poor Galaxy

Q: Is there any information which explains the jargon used in the photometry of objects in NED?A: We encourage our users to go back to the original papers to fully understand the magnitudes adopted by NED. Here are a few examples of magnitudes currently found in NED's detailed photometric data:

u, g, r, i, or z usually refers to the five-band SDSS photometric
system

B is a B-band magnitude on the Johnson system

BT is a total magnitude in the B-band

BT0 is a total magnitude in the B-band corrected
to "face-on" (i.e. inclination = 0 degrees)

bj is approximately a B magnitude derived from photometry
on a IIIa-J plate

R25 is an R magnitude at the 25th mag arcsec-2
isophote level

J, H, or Ks usually refers to the three-band 2MASS photometic
system

Q: The fields of view from the 2MASS Large Galaxy Atlas (LGA) do not agree between the FITS and GIF versions of the images. Which is correct?A: Both; each is correctly labeled. The FITS images cover the entire image from the LGA, while the GIF images typically cover only the inner parts of the FITS images. The GIFs are used for the quick-look thumbnails in the image list; while the FITS images always cover the entire galaxy, and are suitable for scientific use.

Q: What are the object type codes that NED uses?A: Here is the current list of object types used in NED, listed alphabetically (objects within the Milky Way Galaxy have their types preceded by an exclamation point "!"):

*

Star or Point Source

**

Double star

*Ass

Stellar association

*Cl

Star cluster

AbLS

Absorption line system

Blue*

Blue star

C*

Carbon star

EmLS

Emission line source

EmObj

Emission object

exG*

Extragalactic star (not a member of an identified galaxy)

Flare*

Flare star

G

Galaxy

GammaS

Gamma ray source

GClstr

Cluster of galaxies

GGroup

Group of galaxies

GPair

Galaxy pair

GTrpl

Galaxy triple

G_Lens

Lensed image of a galaxy

HII

HII region

IrS

Infrared source

MCld

Molecular cloud

Neb

Nebula

Nova

Nova

Other

Other classification (e.g. comet; plate defect)

PN

Planetary nebula

PofG

Part of galaxy

Psr

Pulsar

QGroup

Group of QSOs

QSO

Quasi-stellar object

Q_Lens

Lensed image of a QSO

RadioS

Radio source

Red*

Red star

RfN

Reflection nebula

SN

Supernova

SNR

Supernova remnant

UvES

Ultraviolet excess source

UvS

Ultraviolet source

V*

Variable star

VisS

Visual source

WD*

White dwarf

WR*

Wolf-Rayet star

XrayS

X-ray source

!*

Galactic star

!**

Galactic double star

!*Ass

Galactic star association

!*Cl

Galactic Star cluster

!Blue*

Galactic blue star

!C*

Galactic carbon star

!EmObj

Galactic emission line object

!Flar*

Galactic flare star

!HII

Galactic HII region

!MCld

Galactic molecular cloud

!Neb

Galactic nebula

!Nova

Galactic nova

!PN

Galactic planetary nebula

!Psr

Galactic pulsar

!RfN

Galactic reflection nebula

!Red*

Galactic red star

!SN

Galactic supernova

!SNR

Galactic supernova remnant

!V*

Galactic variable star

!WD*

Galactic white dwarf

!WR*

Galactic Wolf-Rayet star

Q: Why doesn't NED have any information about the Sun, the planets, or the stars?A: NED is an extragalactic database. Data and references for Galactic objects may be retrieved from SIMBAD,
maintained by the Centre de Donnees astronomiques de Strasbourg, France. Solar system and planetary data may be retrieved from NASA's Planetary Data System at JPL.

Q: What images are included in NED?A: Most of the images NED holds on line are optical, infrared, and radio images of galaxies, though we do have some UV and X-ray images as well. We also collect HI spectra, isophote maps, and other graphical representation of extragalactic data. NED can also display an image of a given object from the Digitized Sky Survey using one of the Object Search options, or the Image Search option, all available on NED's Home Page.

Q: How may I contribute my data (catalogs, FITS images or spectra) to NED?A: Please leave a comment with your name and email address so that we may contact you.

Q: Why is it that not all of the IRAS catalog entries are in NED?A: When we loaded the IRAS catalogs, we used various filters to improve the chances of a source being extragalactic.

FSC sources in NED were chosen using the following "color" and quality constraints:
1) F(25)/F(60) < 2.0 AND
2) Q(60) ≥ 3
PSC sources used the same flux and color filters, and added three additional filters based on the IRAS "cirrus" flags:
1) cirr1 < 9 AND
2) cirr2 < 7 AND
3) cirr3 < 75
In addition, all PSC sources in the areas of the LMC, SMC,
M31, and M33 were loaded into NED and flagged as being within
the boundaries of those galaxies.

Q: There are only 1500 entries in the Markarian catalog. Yet NED has some Markarian numbers over 1500. Where do these extra numbers come from?A: In 1986, V. A. Lipovetsky and J. A. Stepanian collected all the Markarian objects from the fifteen published lists into a complete "First Byurakan Survey." This list, never published but privately circulated, included an additional 32 objects given provisional numbers from 9001 to 9032. A few of these provisional numbers have appeared in the
literature, so we have put all of them into NED. Then, in 1989, Markarian, Lipovetsky, Stepanian, L. K. Erastova, and A. I. Shapovalova published their complete Markarian catalog in Communications of the Special Astrophysical Observatory, No. 62 as "The First Byurakan Survey. A Catalogue of Galaxies with UV-continuum." This catalog has an additonal 15 objects numbered from 1501 to 1515, 14 from the 32 new objects in the 1986 list, and one new. We have also put these 15 numbers into NED, so the 14 new objects in common to the 1986 and 1989 lists carry two Markarian numbers.

Q: There is a gap in the Fairall numbers between 1185 and 1201. Do these objects exist?A: No. Fairall's original lists (see Fairall, MNRAS 233, 691, 1988 and references therein) contained data for 1185 compact and bright-nucleus galaxies, while the latest paper (Fairall and Woudt, MNRAS 366, 267, 2006) has data for 336 galaxies found in large-scale structures across the sky near the South Celestial Pole. The two samples are thus independent. Therefore, Fairall started his numbers for his latest large-scale structure sample at 1201 to avoid confusion between it and his earlier sample of compact galaxies.

Q: The RC3 data in NED sometimes do not agree with the RC3 printed version. Why?A: NED's version of RC3 (the Third Reference Catalogue of Bright Galaxies) includes the many corrections detailed in Corwin et al. AJ 108, 2128, 1994 as well as a few others made since that paper was published.

Q: DSS images of some galaxies near the celestial poles are rotated with respect to 2MASS images. Which image is correct?A: The 2MASS images are correctly oriented. The direction of north on the DSS images is dependent on several factors, including their position on the original 6.4 x 6.4-degree sky survey plate, the epoch of the original plate, and the software used for scanning and image extraction. The 2MASS images come directly from the sky at an epoch very close 2000.0, so were processed with equinox J2000.0 coordinates.

The NASA/IPAC Extragalactic Database (NED) is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.